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Wai-Choong Wong

Bio: Wai-Choong Wong is an academic researcher from National University of Singapore. The author has contributed to research in topics: Network packet & Throughput. The author has an hindex of 29, co-authored 254 publications receiving 3580 citations. Previous affiliations of Wai-Choong Wong include Institute for Infocomm Research Singapore & Bell Labs.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors explore techniques for replacing missing speech with wave-form segments from correctly received packets in order to increase the maximum tolerable missing packet rate in voice communications.
Abstract: Packet communication systems cannot, in general, guarantee accurate and prompt delivery of every packet. The effect of network congestion and transmission impairments on data packets is extended delay; in voice communications these problems lead to lost packets. When some speech packets are not available, the simplest response of a receiving terminal is to substitute silence for the missing speech. Here, we explore techniques for replacing missing speech with wave-form segments from correctly received packets in order to increase the maximum tolerable missing packet rate. After presenting a simple formula for predicting the probability of waveform substitution failure as a function of packet duration and packet loss rate, we introduce two techniques for selecting substitution waveforms. One method is based on pattern matching and the other technique explicitly estimates voicing and pitch. Both approaches achieve substantial improvements in speech quality relative to silence substitution. After waveform substitution, a significant component of the perceived distortion is due to discontinuities at packet boundaries. To reduce this distortion, we introduce a simple smoothing procedure.

247 citations

Journal ArticleDOI
TL;DR: A comprehensive classification of various IDS approaches according to their employed detection techniques is presented, and the three main categories explored in this paper are anomaly detection, misuse detection, and specification-based detection protocols.
Abstract: This paper surveys recently proposed works on Intrusion Detection Systems (IDS) in WSNs, and presents a comprehensive classification of various IDS approaches according to their employed detection techniques. The three main categories explored in this paper are anomaly detection, misuse detection, and specification-based detection protocols. We give a description of existing security attacks in WSNs and the corresponding proposed IDS protocols to tackle those attacks. We analyze the works with respect to the network structure of WSNs. In addition, we highlight various critical shortcomings that IDSs currently have and define future research tracks for IDSs in wireless sensor networks. Though a few restricted survey works on this topic have already been done, we feel that there is a great need of performing a detailed and comprehensive study on the vital aspects so that the IDS in WSN could be analyzed from all the `need-to-know' angles. Thus, the paper's main aim is to include the most recent advancements in this area as well as to predict the future course of research so that the general as well as expert readers could be greatly benefited.

208 citations

Proceedings ArticleDOI
21 Mar 2011
TL;DR: A robust DR pedestrian tracking system on top of such commercially accessible sensor sets capable of DR, exploiting the fact that, multiple DR systems, carried by the same pedestrian, have stable relative displacements with respect to the center of motion, and therefore to each other.
Abstract: The emergence of personal mobile device with low cost sensors, such as accelerometer and digital compass, has made dead-reckoning (DR) an attractive choice for indoor pedestrian tracking. In this paper, we propose a robust DR pedestrian tracking system on top of such commercially accessible sensor sets capable of DR. The proposed method exploits the fact that, multiple DR systems, carried by the same pedestrian, have stable relative displacements with respect to the center of motion, and therefore to each other. We first formulate the robust tracking task as a generalized maximum a posteriori sensor fusion problem, and then we narrow it to a simple computation procedure with certain assumptions. A prototype is implemented and evaluated with a benchmark system that collects ground truth efficiently and accurately. In a practical indoor testbed, the proposed scheme has exhibited robust tracking performance, with reduction in average tracking error up to 73.7%, compared to traditional DR tracking methods.

170 citations

Patent
16 Nov 1994
TL;DR: In this article, a shared time-division duplexing (STDD) scheme is proposed to allow both uplink and downlink voice traffic to share a common channel by dynamically allocating time slots in the common information channel.
Abstract: A low delay multiple access scheme called Shared Time-Division Duplexing (STDD), allows both uplink and downlink voice traffic to share a common channel. The scheme contains separate uplink and downlink control channels and a common voice information channel. The control channels comprise means for signalling voice requirements and acknowledgements of the time slot allocation. Using speech activity detection only, talk spurt speech packets are generated for transmission. STDD dynamically allocates time slots in the common information channel taking advantage of co-ordinated two-way conversations to achieve high statistical multiplexing gain and more efficient realization of the common information channel.

164 citations

Journal ArticleDOI
TL;DR: The teletraffic performance of a highway microcellular digital mobile radio system having an oversailing macrocell that spans many microcells is presented and a narrowband time-division-multiple-access arrangement supporting ten channels per carrier and one carrier per base station is used.
Abstract: The teletraffic performance of a highway microcellular digital mobile radio system having an oversailing macrocell that spans many microcells is presented. The microcellular cluster is composed of concatenated segments of the highway where each segment is a microcell, typically 500-2000 m in length, with the base stations located at lamp-post elevations. A narrowband time-division-multiple-access arrangement supporting ten channels per carrier and one carrier per base station is used. The teletraffic analysis assumes there are n-up and n-down lanes, and that the vehicular speeds conform to a truncated Gaussian distribution whose mean speed is 100 or 50 km/h when the vehicular traffic is free-flowing or in traffic-congested conditions, respectively. >

156 citations


Cited by
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Proceedings ArticleDOI
22 Jan 2006
TL;DR: Some of the major results in random graphs and some of the more challenging open problems are reviewed, including those related to the WWW.
Abstract: We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

7,116 citations

Proceedings Article
01 Jan 1991
TL;DR: It is concluded that properly augmented and power-controlled multiple-cell CDMA (code division multiple access) promises a quantum increase in current cellular capacity.
Abstract: It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

2,951 citations

01 Apr 1997
TL;DR: The objective of this paper is to give a comprehensive introduction to applied cryptography with an engineer or computer scientist in mind on the knowledge needed to create practical systems which supports integrity, confidentiality, or authenticity.
Abstract: The objective of this paper is to give a comprehensive introduction to applied cryptography with an engineer or computer scientist in mind. The emphasis is on the knowledge needed to create practical systems which supports integrity, confidentiality, or authenticity. Topics covered includes an introduction to the concepts in cryptography, attacks against cryptographic systems, key use and handling, random bit generation, encryption modes, and message authentication codes. Recommendations on algorithms and further reading is given in the end of the paper. This paper should make the reader able to build, understand and evaluate system descriptions and designs based on the cryptographic components described in the paper.

2,188 citations

Journal ArticleDOI
TL;DR: It is discussed, how blockchain, which is the underlying technology for bitcoin, can be a key enabler to solve many IoT security problems.

1,743 citations

Journal ArticleDOI
01 May 1998
TL;DR: In this paper, a review of error control and concealment in video communication is presented, which are described in three categories according to the roles that the encoder and decoder play in the underlying approaches.
Abstract: The problem of error control and concealment in video communication is becoming increasingly important because of the growing interest in video delivery over unreliable channels such as wireless networks and the Internet. This paper reviews the techniques that have been developed for error control and concealment. These techniques are described in three categories according to the roles that the encoder and decoder play in the underlying approaches. Forward error concealment includes methods that add redundancy at the source end to enhance error resilience of the coded bit streams. Error concealment by postprocessing refers to operations at the decoder to recover the damaged areas based on characteristics of image and video signals. Last, interactive error concealment covers techniques that are dependent on a dialogue between the source and destination. Both current research activities and practice in international standards are covered.

1,611 citations